[ovs-dev] [PATCH RFC] dpif-netlink: distribute polling to discreet handlers

Matteo Croce technoboy85 at gmail.com
Fri Jun 26 00:07:48 UTC 2020


On Wed, Jun 24, 2020 at 3:48 PM Aaron Conole <aconole at redhat.com> wrote:
>
> Currently, the channel handlers are polled globally.  On some
> systems, this causes a thundering herd issue where multiple
> handler threads become active, only to do no work and immediately
> sleep.
>
> The approach here is to push the netlink socket channels to discreet
> handler threads to process, rather than polling on every thread.
> This will eliminate the need to wake multiple threads.
>
> To check:
>
>   ip netns add left
>   ip netns add right
>   ip link add center-left type veth peer name left0
>   ip link add center-right type veth peer name right0
>   ip link set left0 netns left
>   ip link set right0 netns right
>   ip link set center-left up
>   ip link set center-right up
>   ip netns exec left ip link set left0 up
>   ip netns exec left ip addr add 172.31.110.10/24 dev left0
>   ip netns exec right ip link set right0 up
>   ip netns exec right ip addr add 172.31.110.11/24 dev right0
>
>   ovs-vsctl add-br br0
>   ovs-vsctl add-port br0 center-right
>   ovs-vsctl add-port br0 center-left
>
>   # in one terminal
>   perf record -e sched:sched_wakeup,irq:softirq_entry -ag
>
>   # in a separate terminal
>   ip netns exec left arping -I left0 -c 1 172.31.110.11
>
>   # in the perf terminal after exiting
>   perf script
>
> Look for the number of 'handler' threads which were made active.
>
> Reported-by: David Ahern <dsahern at gmail.com>
> Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2019-December/365857.html
> Cc: Matteo Croce <technoboy85 at gmail.com>
> Cc: Flavio Leitner <fbl at sysclose.org>
> Signed-off-by: Aaron Conole <aconole at redhat.com>
>

Great work!

Just to understand, this reverts some logic of my patch, and
transposes the threads and sockets?

Maybe it's the case to add a Fixes tag pointing to 69c51582f ?

Nitpick: `iproute -n` instead of `ip netns exec` where possible, e.g.

ip netns exec left ip link set left0 up

becomes

ip -n left link set left0 up

Cheers,
-- 
Matteo Croce

perl -e 'for($t=0;;$t++){print chr($t*($t>>8|$t>>13)&255)}' |aplay


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